Have connectivity self-register manager classes

As connectivity services are planned to move to a separate module, move
the manager classes registration from SystemServiceRegistry to
ConnectivityServicesRegistrar, using the registerContextAwareService
APIs.

This follows patterns and naming in WifiFrameworkInitializer.

Bug: 171540887
Test: device boots, connectivity working
Change-Id: I62ced1275750c73f209bac8ec3a3204b95695b83